1. Field of Invention
The present invention relates to a coupling network, and more particularly to an AC coupling integrating network for a burst optical receiver which is adapted to enhance the sensitivity thereof as compared with conventional AC coupling networks in conventional optical receivers.
2. Description of Related Arts
With the development of information technology, the utilization of optical fibers for the purpose of data transmission has become extremely popular. For example, data transmission for the purpose of internet connection has been one of the major applications of optical fibers. Other applications include telephone signal transmissions as well as cable broadcast.
No matter which particular form of application the optical fibers are utilized, a typical optical signal transmission system is faster than a traditional cable transmission system or a DSL transmission system, wherein the PON (Passive Optical Network), which has been widely considered as the next generation superstar in the communication business, is adapted with point-to-multi-point technology with bi-directional structure instead of the traditional point-to-point inefficient network, which means the single OLT (Optical Line Terminal) broadcasts the data on the single optical cable through a splitter to the multiple ONUs (Optical Network Unit) to complete the download process while the multiple ONUs upload the data to the OLT on the single optical cable to complete the upload process.
The goal of FTTH (Fiber to the Home) is therefore procurable by minimizing the cost of the infrastructure of the optical fiber network and offering a reasonable price for general public usage. In order to implement the bi-directional PON, the WDM (Wavelength Division Multiplexing) for the download process and the TDM (Time Division Multiplexing) for the upload process emerge as the breakthrough technology for exploiting the capacity of the optical fiber, wherein the TDM facilitates different time slots for each ONU user to upload data to the OLT on the same optical fiber and consequently the total number of ONU on the same cable is limited by the duration of each time slot, which theoretically the infinitesimal duration of each time slot achieves maximum total number of time slot to increase the data throughput.
The burst mode transceiver is employed in minimizing the duration of each time slot, wherein the burst mode transmitter transmits optical signals in burst form which is received by the burst mode optical receiver via the optical fibers. The burst mode optical receiver is adapted to convert burst optical signal to a suitable electric signal and transmit the electric signal to the relevant application terminal.
Thus, one may appreciate that the extent to which the application terminal is capable of performing optimally would largely depend upon the quality of the electric signal as converted by the burst optical receiver. However, as a matter of fact, when the burst mode optical signal is transmitted via the optical fibers, there exist considerable amount of noise interfering with the optical signal so as to affect the conversion of the optical signal to the electric signal. For example, the DC offset problem; jittering and distortion; the SNR (Signal to Noise Ratio) where the amplitude of noise is comparable with the optical signal which is to be transmitted, the optical receiver is difficult to recognize so that the resulting converted electric signal may simply be different from the electric signal which would have been correctly converted.
A difficult scenario for those skilled in the art is that in order to achieve a satisfactory electric signal, the extinction ratio of the optical signal needs to be high such that the effect of interference from the noise for the purpose of signal conversion can be minimized. Though this may bring a satisfactory solution from the viewpoint of signal conversion, an increase of extinction ratio can cause other problems. For instances, setting the extinction ratio too high may overload the entire circuitry of the optical receiver as well as the optical fibers so as to reduce the general lifespan of the relevant electrical components. However, a lower extinction ratio may blur the distinction between noise and the optical signal so that the burst optical receiver is incapable of properly convert the optical signal into a desirable electric signal.
As an attempt to balance the above conflicting technical requirements, conventional burst optical receivers are usually low in sensitivity and speed. For example, the sensitivity of a conventional optical receiver is usually in the range of −29 dBm at 155 Mb/sec, which should have been increased for enhancing the terminal applications.